Risk of juvenile idiopathic arthritis among children conceived after fertility treatment: a nationwide registry-based cohort study.

STUDY QUESTION: Is the risk of juvenile idiopathic arthritis (JIA) increased in children conceived after fertility treatment, and is an observed association caused by specific types of fertility treatment or by factors associated with the underlying infertility? SUMMARY ANSWER: The risk of JIA in children conceived after fertility treatment (any and specific types of fertility treatment) was not convincingly affected when compared with children born to fertile women. WHAT IS KNOWN ALREADY: It has been suggested that fertility treatment may affect the development of the immune system and thereby increase the risk of developing autoimmune diseases, including JIA. STUDY DESIGN, SIZE, DURATION: This retrospective population-based cohort study included all live-born children in Denmark between 1 January 1996 and 31 December 2012 (n = 1 084 184). The study population was followed from date of birth until first diagnosis of JIA as registered in the Danish National Patient Registry, date of 16th birthday, date of emigration, date of death or end of follow-up (31 December 2014), whichever occurred first.